The structure and principle of ultrasonic welding machine
The ultrasonic welding machine is mainly composed of the following parts: generator, pneumatic part, program control part, and transducer part. The main function of the generator is to convert the 50Hz power supply with electronic circuits into high-frequency (for example, 20KHz) high-voltage electric waves; the main function of the pneumatic part is to complete the pressure work requirements such as pressure and pressure during the processing; program control The part controls the working process of the whole machine to achieve consistent processing effect; the part of the transducer converts the high-voltage electric wave generated by the generator into mechanical vibration, which is transmitted and amplified to reach the processing surface.
There are generally two types of generators that are widely used in China: One is the bridge power amplifier circuit used by the United States BRANSON company, the protection circuit adopts phase protection, and the operating frequency is generally 20KHz. Its advantage is high electrical conversion efficiency. The disadvantage is that the frequency adjustment inductance adjustment range is narrow and the frequency tracking performance is poor; the other disadvantage is that the power cannot be made large, the maximum is about 3KW; the other is a Taiwanese machine, which is common Use class B power amplifier, overcurrent protection, bridge feedback. The advantage is that the power can be made larger (such as 4.2KW), the frequency tracking performance is good, and the working frequency of 15KHz is generally used in the case of high power. The disadvantage is that the electrical conversion efficiency is low, and the working frequency of 15KHz is audible to the human ear, reflecting the greater noise; in addition, there are machines using automatic frequency tracking technology in Switzerland, Germany, and Japan. Because of its high price, it is not common in China.
The transducer part is composed of three parts: transducer (TRANSDUCER), amplifier (also called secondary pole, horn, BOOSTER), welding head (also called welding die, HORN or SONTRODE).
① Transducer (TRANSDUCER): The role of the transducer is to convert electrical signals into mechanical vibration signals. There are two physical effects that can be applied to convert electrical signals into mechanical vibration signals. A: Magnetostrictive effect. Magnetostrictive effect is commonly used in early ultrasonic applications. Its advantage is that it has a large available power capacity; its disadvantage is that it is low in conversion efficiency, difficult to manufacture, and difficult to mass industrial production. B: The reverse effect of the piezoelectric effect. Piezoelectric ceramic transducers have the advantages of high conversion efficiency and mass production. The disadvantage is that the power capacity produced is relatively small. The existing ultrasonic machines generally use piezoelectric ceramic transducers. The piezoelectric ceramic transducer is made by sandwiching the piezoelectric ceramic between two metal front and rear load blocks and tightly connected by a screw. The output amplitude of a typical transducer is about 10 μm.
② BOOSTER: The horn itself is a metal column. Through the design of the shape, the amplitude transmitted by the transducer can be amplified to achieve the energy amplitude required for processing plastic parts, which is equivalent to the heating temperature, such as The processing amplitude required for our commonly used ABS and AS plastics is about 20μm; the processing amplitude required for nylon and polypropylene is about 50μm.
③ HORN: The function of the welding head is to make specific plastic parts and meet the requirements of the shape and processing range of the plastic parts.
The transducers, horns, and welding heads are all designed to be half the wavelength of the working ultrasonic frequency, so their size and shape must be specially designed; any modification may cause changes in frequency and processing effects, so it is necessary Professional production. Depending on the material used, the size will vary. Materials suitable for ultrasonic transducers, horns and welding heads are: titanium alloy, aluminum alloy, alloy steel, etc. Because ultrasonic waves vibrate constantly at a high frequency of about 20KHz, the requirements for materials are very high, which is not what ordinary materials can withstand.